How does a tree know when to stop growing a branch and start growing a leaf?

Question

How does a tree know when to stop growing a branch and start growing a leaf?

In: Biology

Answer 1

It doesn’t really, trees work like this:

There is something called the apical meristem that is basically like a bundle of stem cells inside the trunk near the top of the tree. It sends out cells and signals that grow into the new branches, but it also sends out another chemical that goes back down the trunk towards the ground and inhibits any new branches from growing lower. This system keeps all the new branches growing at the top of the tree where they’ll be in the sunlight and grow leaves.

All the branches also have meristems at the tip kinda like the one in the trunk so that same chemical inhibitor decreases as the branches grow longer until it is low enough a new twig starts growing and branching off. The direction of the growing branches is determined by the sun – tree cells have things that work as sensors to detect sunlight and temperature and these sensors trigger a bunch of systems that cause the branches to grow towards the most light. They can’t grow forever because in addition to photosynthesis the tree cells need a bunch of nutrients from the ground to survive. Trees have a system of basically tubing running up the trunk that sorta sucks water out of the ground and physics stuff like width of the tube determines how high it can go and how far it can get out through the branches. Beyond that new stuff won’t grow because the nutrients the cells need to grow aren’t there.

Like mentioned just above the cells have a method of sensing both temperature and sunlight. There’s a complex system of stuff that happens from the interaction of these sensors, where a certain amount of sunlight and multiple days above a minimum temperature causes changes in these systems that cause buds to start growing. The branches further down the trunk already stopped growing because of the chemical inhibitor and if the cells in these branches don’t sense enough sunlight they just won’t grow buds. The growing branches continue growing.